1. Field of Invention
The present invention relates to an integrate circuit chip. More particularly, the present invention relates to a chip with stacked magnetic devices.
2. Description of Related Art
Magnetic devices may be used as magnetic memory cells to stored data in a non-volatile fashion, which means the data written into the memory cells stays in the memory cells whether or not the circuit is powered. Therefore, magnetic devices are used as non-volatile memory elements such as flash memory, SRAM, DRAM, cache memory, hard drives . . . etc. Not only does the magnetic devices be able to serve as memory elements, they may function as digital switches. The directions of the dipoles in the two magnetic layers of a magnetic device determines the conductivity of the device, thus the conductive state may be the “on” state of the switch, and the non-conductive state may be the “off” state of the switch.
The magnetic switches may be used to build logic gate as well as the transistors may be used. Conventional transistor logic gates are volatile, therefore, for example, if a system using field programmable gate array (FPGA) is built with transistor gates, separate system chips are required to store the program to implement the functions required. At, boot up, the FPGA needs to be reprogrammed to fit the task at hand. Performance of the FPGA system suffers due to these requirements.
Furthermore, transistor logic has a circuit density limit which the placement of the devices needs to be spread out due to routing concerns. Also, since transistor logic may only be implemented on the layer above the silicon substrate thus the integration of a large number of function blocks may not be practical due to chip area concerns.
For the forgoing reason, there is a need for a new logic design structure to reduce circuit density and integrate more function block such as CPU, memory, and logic gate arrays into a single chip.